GRPR and cancer: In view of the overexpression of the gastrin-releasing peptide receptor (GRPR, bombesin-2 receptor) at a high density and frequency already in early stages of prostate cancer (∼5,000 disintegrations/min [dpm]/mg of tissue, with >2,000 dpm/mg being considered clinically relevant) and breast cancer (∼10,000 dpm/mg), GRPR has been identified as a promising target for both cancer types (3,4).